Air Compressor Capacity Unit

If you define the standard temperature and pressure condition then you have to calculate the capacity based on these values.

But you can nominate any other condition and calculate the capacity for the new condition.

There might be different values for different conditions.

The key is the PVT (pressure volume temperature) constant.

In general capacity should be given for standard conditions.

This is done because the volume of a gas is dependent on the pressure and temperature. I have worked with natural gas, and there, we use SCFM and ACFM to differentiate between standard and actual flow rates.

Standard cubic feet per minute (SCFM) is the volumetric flow rate of a gas corrected to "standardized" conditions of temperature and pressure, making it the equivalent of the mass flow rate of the gas

thanks to all.

The actual concern is, I am calculating the capacity of a compressor based on inputs available from various users. The consumption unit varies from Nm3/hr to m3/hr.

When i calculate the capacity in terms of Nm3/hr, my superior asks for a reference back up which defines the NTP state which is not available. this makes me to use STP condition as it is defined in CAGI handbook.

Now my confusion is if i use STP as i mentioned in my 1st post, then the capacity of the compressor should it be SCFM or Sm3/hr.

1 of my user has also provided consumption as Nm3/hr but has stated the condition as 1bar and 20deg. C.

This is the cause of my confusion. Using the best engineering practise is good, but satisfying my superior with jus that is not working out.

Thanks again.

varun

Thanks again Economist.

Will remember your explanation.

Varun

For air compressors, the Nm3/h means air temp at 25 deg C, and 1 atm pressure.

The N stands for Normal. Usually, the specs will allways mention the conditions under which the values are given.

For your consumers: You need to clarify the conditions. It is the best way to avoid having confusions. Once the conditions are specified, it does not matter which system of measure you use: the capacity can be m3/h or CFM. Before mentioning S for standard, define the Standard used!(convert CFM to m3/h or vis-versa )

In our organization the Nm3 means gas volume at a temp of 0 deg C, and 1 atm pressure. But I really don't know from which definition we follow.

There must be an international agreement to normalise the definitions.

Compressed Air equipment manufacturers normally use Normal as being either 15 drg C or 25 deg C, and Usually under 1 atm pressure.

But you can check and ask the supplier (or the specifiers) to clarify their definition.

Sorry for the late reply.

Thanks to all for their replies. It is better to formalize the conditions.

However use of different standards opt for different values.

Eg. As per CAGI handbook chapter 8, STP is as I mentioned in the 1st post. There are no reference books to define the term NTP (as far as I have googled).

As per IUPAC 1 bar and 0deg.c are STP, which again has been refered to as NTP above.

Anyways thanks to all your valuable replies.